This invention relates to a water-based two-component assembly adhesive with high early tack, at least one component containing a proportion of a low molecular weight compound dissociating in water.
The use of adhesives in the manufacture of industrial goods and in the DIY field is increasingly replacing mechanical fixings and fastenings. This is particularly the case where the joint between two workpieces is only exposed to moderate mechanical loads. So-called assembly adhesives are often distinguished by high early tack, which enables them rapidly to fix even relatively heavy workpieces.
Today, solvent-based assembly adhesives are being increasingly replaced by water-based assembly adhesives. The main advantages of the water-based adhesives over the solvent-based adhesives lie in improved processing properties, increased ageing resistance and, not least, in the absence of environmentally harmful and health-endangering solvents.
However, these advantageous water-based assembly adhesives also have to satisfy requirements in regard to adhesive performance and particularly in regard to the early tack of the assembly adhesive. Where assembly adhesives are used, bonded workpieces generally have to be kept in the required position by mechanical fixing in the initial phase of the bonding process. However, this results in increased effort in the use of assembly adhesives and is often found to be troublesome by users. However, there would be no need for such fixing if the early tack of the assembly adhesives used were high enough.
The early tack of the water-based assembly adhesives known from the prior art is often influenced by the use of thickeners, which, unfortunately, greatly increase the viscosity of the adhesives. This high viscosity necessitates correspondingly resistant, high-performance stirrers, which are capable of reliably mixing such highly viscous products. However, the performance of the mixers/stirrers for adhesives imposes a limit on known assembly adhesives in regard to their viscosity and hence in regard to the strength of the early tack.
In addition, however, an upper limit is also placed on the maximum viscosity by the processing properties of such adhesives. Even the discharge of high-viscosity adhesives from an appropriate container, for example a tube or a cartridge, can be complicated by an excessive viscosity of the adhesive to such an extent that, despite possibly high early tack, the user finds this to be such a disadvantage that he turns to other products.
DE 691 10 403 T2 describes aqueous suspensions of nonionic polymers in a salt medium. The described suspensions contain, for example, cellulose derivatives as the nonionic polymers and sodium formate as the salt, the suspensions having to contain at least 28% by weight sodium formate. However, salt concentrations as high as these are not suitable for the use of the described suspensions in two-component adhesives.
DE 689 18 789 T2 relates to a suspension of water-soluble polymers in aqueous media containing dissolved salts and describes, for example, suspensions of cellulose derivatives in aqueous solutions of ammonium salts, the ratio by weight of ammonium salt to water being at least 0.15:1. However, the described salt concentration is too high for the use of the described suspensions in two-component adhesives.
DE OS 2 417 086 relates to additives for mortars and concrete in the form of aqueous dispersions and describes aqueous dispersions of water-soluble substances, the dispersion medium used being a solution of salts or organic solvents in which the substances are insoluble or only partly soluble. According to the Examples, a 25% by weight solution of aluminium sulfate, for example, is used for the dispersion of hydroxyethyl cellulose while an ethylene oxide polymer is dispersed in a 15% by weight solution of sodium sulfate. The described dispersions are also unsuitable for use in two-component adhesives.
DE 101 16 023 discloses, for example, a water-based assembly adhesive based on an aqueous styrene/alkyl acrylate dispersion. The use of salts is not mentioned in this document.
Besides liquid, water-based assembly adhesives, assembly adhesive powders are known from the prior art and have to be mixed with a suitable solvent by the user before application. However, adhesive powders have disadvantages in regard to storage and application. On the one hand, the processing of such fine powders is attended by the emission of dusts, which are harmful to health if inhaled; on the other hand, unwanted lumps are also easily formed when the powder is mixed in a solvent.
Accordingly, there was a need for assembly adhesives, which would show, improved early tack in relation to known assembly adhesives.
In addition, there was a need for assembly adhesives, which, despite high early tack, would still allow correcting movements to be made at the beginning of the bonding process.
There was also a need for assembly adhesives, which would be simple and safe to use.
There was also a need for environmentally friendly and physiologically safe assembly adhesives.
In addition, there was a need for assembly adhesives with high early tack, which would be easy to discharge from a corresponding adhesive container with little effort.
There was also a need for a process for the production of assembly adhesives with improved early tack, which, in addition, would optionally be easy to handle, environmentally friendly and physiologically safe.
Accordingly, the problem addressed by the present invention was to provide assembly adhesives which would satisfy one or, more preferably, more or all of the above-mentioned requirements.